1. Field of the Invention
The present invention relates to the treatment of stack gases and waste water streams and, more particularly, to a simultaneous process for removing sulfur dioxide from such gas streams and purifying the waste water streams.
2. Brief Description of the Prior Art
The burning of fossil fuels such as coal and oil results in the production of sulfur oxides such as sulfur dioxide. Sulfur oxides are formed by oxidation of the naturally occurring sulfur in the fossil fuels. With the energy shortage requiring the use of fossil fuels containing higher and higher amounts of sulfur, methods for the removal of sulfur dioxide from flue or stack gases and the like are becoming increasingly important.
Virtually as severe as the air pollution problem caused by the emission of sulfur dioxide laden stack gases is the pollution problem posed by the disposal of waste water from domestic sewage. The problem is especially acute in densely populated areas where literally millions of gallons of untreated or inadequately treated waste water from such domestic sewage is discharged into streams, lakes and the like. As is well known, the discharge of such inadequately treated waste water can cause severe health problems as well as being esthetically most undesirable.
It is known that SO.sub.2 can be removed from gas streams such as stack gases by the use of aqueous scrubbing mediums containing various amounts of iron. Thus, for example, U.S. Pat. Nos. 2,021,936 to Johnstone and 3,836,630 to Noguchi et al. both teach methods for treating sulfur containing gas streams using scrubbing mediums containing iron. Additionally, U.S. Pat. No. 1,956,420 to Gleason et al. is typical of prior art which teaches the use of iron and iron salt coagulants and flocculants for the removal of suspended solid matter from waste water derived from raw sewage. None of the patents disclosed above teach the simultaneous treatment of sulfur dioxide laden stack gases and waste water derived from raw sewage so as to, in effect, purify one with the other. U.S. Pat. No. 3,522,173 to Lindman et al. teaches the treatment of waste water by the use of sulfur dioxide as an acidifying agent and iron as a flocculating agent to purify the waste water. However, the Lindman et al. method requires admixing the SO.sub.2 gas stream with large amounts of oxygen or oxygen containing gases for the method to be effective. Moreover, the Lindman et al. process is limited to the use of gas streams containing limited amounts of SO.sub. 2. Thus, the Lindman et al. method is not generally applicable as a stack gas purification method absent careful control of the SO.sub.2 content of the stack gas.